Present Remote Radio Units (RRUs) on the telecom market are normally cooled down through Natural Convection Cooling (NCC) of a heat sink. The solutions discussed herein are exemplified by applications at first hand in conjunction with RRUs. This is however no limitation of the herein provided solutions for enhanced cooling.
The heat sink is typically thermally connected to a heat source for which cooling is crucial, such as a power amplifier of a RRU. The heat sink may typically be made of a heat conducting material such as e.g. copper, aluminium or an alloy comprising any of these or other heat conducting metal. Further, the heat sink may comprise a heat sink base and heat sink fins in order to increase the surface area of the heat sink and thereby the interface area between the heat sink and the environment, available for natural convection. An arbitrary example of such previously known heat sink is schematically illustrated in FIG. 9.
Natural convection cooling is reliable, does not require maintenance or electricity consumption as it has no moving parts and is completely silent.
A disadvantage however with natural convection cooling is the limited cooling capacity (limited to about 20 W/L), which thereby also puts a limit on the transmission capacity of an RRU.
Another disadvantage with natural convection cooling is that natural convection is very low when the RRU is applied indoors, even if most RRUs are mounted outdoors, typically on an elevated location such as a tower, a pole or the roof or wall of a building.
Also, the cooling effect of the heat sink is proportional to the size of the heat sink surface area. A compact design of the RRU and the heat sink is normally desired.
Due to escalating demands for radio capacity of wireless telecommunications, the increase of radio capacity of the RRU is a very important issue for any telecom equipment provider. However, with increased radio capacity of the RRU, normally also the heat generation of the RRU, e.g. of comprised power amplifiers and other components will increase, leading to an increased need for improved heat dissipation.
Increased cooling capacity of the RRU is very important for reliable expanding of mobile network supporting modern 3G, 4G and in future 5G mobile communication standards.
To overcome such limitation in cooling capacity, the convection may be increased by using one or more fans to move air across the surface of the heat sink. An example of such known heat sink with fan-enhanced convection is illustrated in FIG. 10.
However, cooling systems based on conventional fans have many disadvantages.
A main problem of such fan cooling solution is the limited reliability and expected lifetime of the fan. Also the bearings of the rotating fan have a limited lifetime, which bring additional manual maintenance requirements. As stated above, RRUs are typically mounted on elevated location such as towers etc., which makes human maintenance inconvenient, time consuming and dangerous.
Also, the rotating fan causes an aerodynamic noise as well as operating sound of the fan itself, which may be more or less obtrusive. Rotating fans sometimes generate a multitude of low frequency noise, which is often causing noise nuisance complaints.
In case of fan failure, noise and/or vibrations from the fan/bearings may increase and add even more noise pollution to the environment. Further, in case of fan failure natural convection cooling is not very well supported as the fan unit blocks the air flow of the heat sink. Thus a fan failure may lead to overheating of the RRU, or parts thereof.
In order to avoid or at least postpone fan failure and manual maintenance due to fan failure, two or more fans may be utilised for cooling the heat sink, providing some redundancy. However, thereby also the production costs increases.
These serious disadvantages of fan cooling results in that mobile operators increasingly often prefer natural convection cooling instead of fan cooling for their remote radio and other antenna close products, even if this limits the transmission capacity within the communication system.
It would for these reasons be desired to achieve a cooling system for cooling or thermal moderation, in particular for a heat source comprising radio equipment and/or sensitive electronic equipment, having the high reliability, low noise level, low costs, low demands for maintenance and low energy consumption of natural convection cooling, but having an increased cooling capacity, such as e.g. 30-40 W/L or more. It would also be desirable if such an improved cooling system could be mounted on existing heat sinks designed for fan cooling, in order not to have to change, or redesign the heat sink in order achieve the increased cooling capacity.